The present invention relates to coagulation baths for spinning processes.
Cellulose and other polymers can be dissolved in suitable solvents and transferred by controlled solidification into a desired shaped article. If this shaped article is a yarn, fibril or the like, reference is also made to a spinning process. Cellulose is dissolved for example in aqueous solutions of amine oxides, in particular of solutions of N-methylmorpholine N-oxide (NMMO), in order to produce spinning products, such as filaments, staple fibres, films, etc., from the obtained spinning solution. This occurs by precipitation of the extrudates in water or diluted amine oxide solutions once the extrudates of the extrusion die are guided via an air gap into the precipitation bath.
U.S. Pat. No. 4,416,698 relates to an extrusion or spinning method for cellulose solutions in order to shape cellulose into yarns. In this case, a fluid spinning material—a solution of cellulose and NMMO (N-methylmorpholine N-oxide) or other tertiary amines—is shaped by extrusion and solidified and expanded in a precipitation bath. This method is also known as the “lyocell” method.
U.S. Pat. No. 4,246,221 and DE 2913589 describe methods for producing cellulose filaments or films, wherein the cellulose is drawn in fluid form. These documents describe a spinning process in which cellulose is dissolved in tertiary amine oxide, wherein the obtained cellulose solution is pressed via a die, is extruded via an air gap into a spinning funnel, and is discharged at the end of the spinning funnel in the form of continuous yarn. The spinning funnel used is equipped with a feed means and a removal means for the spinning bath.
U.S. Pat. No. 4,261,943 relates to a method for producing shaped cellulose articles, wherein the surface of the spun yarns is treated with a non-solvent.
A further method is described in U.S. Pat. No. 5,252,284, in which elongate shaping capillaries are used to shape a cellulose material.
WO 92/07124 describes a method for producing a cellulose fibre with reduced tendency to fibrillation. The undried fibre is in this case treated with a cationic polymer.
WO 93/19230 A1 describes a further development of the lyocell method, in which the cellulose-containing spinning material is cooled immediately after the shaping process before introduction into the precipitation bath.
WO 94/28218 A1 describes a method for producing cellulose filaments, in which a cellulose solution is shaped into a number of strands via a die. These strands are introduced into a precipitation bath through a gap around which gas flows and are discharged continuously.
DE 555183 relates to spinning vessels for wet spinning, wherein a spinning yarn runs perpendicularly through a number of baths.
WO 92/4871 describes a method for producing a cellulose fibre with reduced tendency to fibrillation. The reduced fibrillation is achieved in that all baths with which the fibre comes into contact before the first drying must have a pH value of at most 8.5. This control in a continuous-flow bath is very complicated and requires chemicals for pH control.
CA 2057133 A1 describes a method for producing cellulose yarns, wherein a spinning material is extruded and is introduced via an air gap into a cooled water bath containing NMMO. To regulate the NMMO constituents, the water bath contains a circuit for bath liquid regeneration with a spinning bath feed and an outlet.
WO 03/014432 A1 describes a precipitation bath with a central device for removing the spinning yarn below a covering film.
DE 10 2004 031 025 B3 discloses a spinning device with a spinning bath containing an inflow chamber for spinning bath liquid, designed to create a laminar spinning bath flow. In this context, a baffle plate is provided for the purpose of preventing the spinning yarns from running into the spinning bath.
EP 1 900 860 A1 describes a 2-step coagulation bath of a spinning device, wherein the baths may contain H2SO4 in different compositions.
U.S. Pat. No. 4,510,111 A relates to a method for producing acrylic yarns, in which a spinning solution is introduced into a first bath immediately, without an air gap.
U.S. Pat. No. 3,851,036 A relates to a spinning method for hollow fibres made from acrylonitriles that can be obtained in a spinning process and by passing them through a plurality of baths.
GB 679 543 A describes a viscose spinning method in a solution counterflow with variable composition.
U.S. Pat. No. 4,056,517 A relates to the spinning of modacrylic copolymers, wherein the spinning yarns are passed through a plurality of baths.
Maron et al. (Lenzinger Berichte, 76 (1997) 98-102), besides the raw material selection, also concerns the coagulation conditions and the influence thereof on NMMO fibres. It is demonstrated that, with highly varying spinning bath concentrations, there is only a very small influence on fibre strength.
Michels and Kosan (Lenzinger Berichte, 86 (2006) 144-153) concerns the coagulation process of cellulose fibres with or without addition of additives formed from spinning solutions consisting of NMMO liquids or ionic liquids. The objective of these examinations is to determine the water retention capacity and the strength of the resultant fibres. The strength of the produced fibres, in accordance with the examples, is largely independent of the solvent used, however additive components (mixed with cellulose) generally cause a considerable decrease in strength. The examples also demonstrate a considerable influence on the water retention capacity of the “never dried” fibre. However, these differences are balanced out to the largest possible extent by one-time drying.
Fink et al. (Lenzinger Berichte, 78 (1998) 41-44) concerns the use of a two-stage precipitation process with use of different precipitants (first stage alcohol, second stage water or aqueous NMMO). Due to this measure, a “skin core” effect is to be achieved, which is to lead to a reduced tendency to fibrillation of the lyocell fibres.